| 摘要 |
PURPOSE:To detect abnormality of sensor by performing air-fuel ratio control while accumulating the lean signal generating time under feedback control region while holding the accumulated level under non-feedback region and performing same air-fuel ratio control with non-feedback upon exceeding over predetermined level. CONSTITUTION:When engine load enters into feedback control region, a controller 44 comprising a microcomputer will accumulate the lean signal generating time from O2 sensor 30 in RAM and hold said accumulated level in such region where feedback through O2 sensor 30 is not performed. When said accumulated level has exceeded over predetermined level during feedback control, it will perform air-fuel ratio control with predetermined air-fuel ratio similarly with non-feedback region irrespective of the output from O2 sensor and reset the accumulated level exceeding over predetermined level through an output from O2 sensor indicating that the air-fuel is over rich. Consequently even if O2 sensor output is abnormal under operating state repeating feedback and non-feedback region, abnormality can be detected reliably and upon continuation of abnormality over predetermined time, it can be transferred to non-feedback control. |
